/*
 * Copyright 2002-2015 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.accept;

import java.util.Collections;
import java.util.List;

import org.springframework.http.HttpHeaders;
import org.springframework.http.InvalidMediaTypeException;
import org.springframework.http.MediaType;
import org.springframework.util.StringUtils;
import org.springframework.web.HttpMediaTypeNotAcceptableException;
import org.springframework.web.context.request.NativeWebRequest;

/**
 * A {@code ContentNegotiationStrategy} that checks the 'Accept' request header.
 *
 * @author Rossen Stoyanchev
 * @since 3.2
 */
public class HeaderContentNegotiationStrategy implements ContentNegotiationStrategy {


	/**
	 * {@inheritDoc}
	 * @throws HttpMediaTypeNotAcceptableException if the 'Accept' header
	 * cannot be parsed.
	 */
	@Override
	public List<MediaType> resolveMediaTypes(NativeWebRequest request)
			throws HttpMediaTypeNotAcceptableException {

		String header = request.getHeader(HttpHeaders.ACCEPT);
		if (!StringUtils.hasText(header)) {
			return Collections.emptyList();
		}
		try {
			List<MediaType> mediaTypes = MediaType.parseMediaTypes(header);
			MediaType.sortBySpecificityAndQuality(mediaTypes);
			return mediaTypes;
		}
		catch (InvalidMediaTypeException ex) {
			throw new HttpMediaTypeNotAcceptableException(
					"Could not parse 'Accept' header [" + header + "]: " + ex.getMessage());
		}
	}

}
